The invention relates to a hemodialysis or hemo(dia)filtration apparatus and a method for controlling the apparatus.
Specifically, though not exclusively, the invention can be usefully employed in any hemodialysis or hemo(dia)filtration apparatus of known type, for example for chronic therapy and/or intensive therapy.
Reference is made in particular to a hemo(dia)filtration at least in post-dilution, i.e. with replacement fluid infusion at least downstream of the semipermeable membrane treatment device (hemo(dia)filter). The present invention can also be applied in hemo(dia)filtration combined with pre- and post-dilution, and in hemo(dia)filtration in mid-dilution, i.e. with replacement fluid infusion between two semipermeable membrane treatment devices arranged consecutively.
As is known, in hemo(dia)filtration a part of the impure plasmatic liquid making up the extracorporeal blood is ultrafiltered through a semipermeable membrane and replaced with the pure replacement fluid. The known art comprises various hemo(dia)filtration systems in which a replacement fluid supply line is connected to a blood circuit downstream of a membrane treatment device. In these systems, when the replacement fluid supply is stopped, there is a tract of extracorporeal circuit (comprised between the membrane and the infusion point) which exhibits very dense blood, being divested of a part of the plasmatic liquid. This leads to the risk of an excessive and undesired increase of the blood pressure in the circuit.
The prior art comprises a hemo(dia)filtration system, known as Gambro® AK 200™, in which on halting the post-dilution flow, the control unit automatically increases the maximum safety value of the venous pressure for a determined period of time, such as to prevent signalling by an alarm due to the fact that it passed beyond the upper limit of the safety range of the venous pressure.
There are also various types of blood treatment systems in which a blood pump is controlled in order to prevent an excessive raising of the extracorporeal blood pressure.
In U.S. Pat. No. 6,083,187, for example, a blood pump is controlled such that the pressure measurements for the blood collection pressure, venous blood pressure and the difference of pressure across a plasma separator do not exceed the respective values.
In EP 1283064, in order to make a further example, a plasma supply pump is controlled in reference to a plasma inlet pressure so that the pressure falls within a predetermined range with respect to a preset pressure value.
EP 1110566 shows a further example in which an extracorporeal treatment system comprises a controller which operates a pump on the basis of a comparison between a measured pressure value and a threshold value.
In WO 03/082144 a blood pump is controlled on the basis of a pressure value in the extracorporeal circuit.
WO 03/028860 describes a hemo(dia)filtration system which comprises automatic passage from a control of a first parameter (for example the blood flow) to the control of a second parameter (for example the blood pressure) when the blood pressure passes out of a respective range of acceptable values.